(a) Field of the Invention
The present invention relates to poly(organophosphazene)-bioactive molecule conjugates in which biodegradable and thermosensitive poly(organophosphazene) with a functional group showing the sol-gel phase transition with change of temperature is combined with various bioactive molecules, such as drugs, a preparation method thereof, and a use thereof for delivery of bioactive molecules.
(b) Description of the Related Art
An aqueous solution of a thermosensitive polymer hydrogel can maintain sol-phase at low temperature, and can be changed into gel-phase by raising the temperature.
Such sol-gel phase transition can occur reversibly. Thermosensitive polymer hydrogel has been considered as a useful delivery material of drugs for injection due to its advantages that the aqueous solution thereof can be easily mixed with therapeutic drugs. Therefore, it can be easily injected into a living body without any surgical operation, and when injected into a desired region of a living body, it forms a gel-phase with a three-dimensional structure at body temperature and is thereby capable of controlled and sustained release of the drugs [Life Science, 65, 261 (1999); J. Control. Rel, 63, 155 (2000)].
However, a problem with drugs with small molecular weights or high hydrophilicity is that they can easily and rapidly pass through the three-dimensional network structure of the gel formed by the thermosensitive polymer hydrogel, causing a large amount of 30% or more of the drugs to be released at an early-stage of the injection. Further, there is another problem that the release of the drug is completed in a short time due to a high rate of diffusion of a hydrophilic drug from the gel into the living body, whereby a sustained release of the drug cannot be achieved (Adv Drug Deliv Rev, 31, 197 (1998)).
Therefore, biodegradable and thermosensitive polymers in which the bioactive molecule or the drug was directly combined with a hydrogel were required. Further, because a cell is unable to grow in the gel, the thermosensitive polymer hydrogel conjugated with the bioactive molecule as the material for the implantation type cell transfer is required.
A copolymer (poloxamer) of the polyethylene oxide and polypropylene oxide is a well known thermosensitive polymer hydrogel. However, the poloxamer is not degradable in vivo [J. Pharm. Pharmacol, 48, 669 (1996)]. In a recent, a biodegradable copolymer (Regel®) of the polyethylene oxide and polylactide acid were reported [Nature, 388, 860 (1997)]. However, Regel® has the disadvantage of not having a functional group, thereby restricting the direct combination with the drugs or bioactive molecules.
The present inventors have reported that poly(organophosphazene) prepared by substitution with an amino acid ester and methoxypolyethyleneglycol in a linear dichlorophosphazene show a thermosensitivity that has a sol-phase in an aqueous solution at a specific temperature or lower, and a phase transition from the sol-phase to the gel-phase of a three-dimensional structure occurs as the temperature is raised above a specific temperature. Further, they are gradually hydrolyzed in an aqueous solution [Macromolecules 32, 2188 (1999); Macromolecules 32, 7820 (1999); Macromolecules 35, 3876 (2002); Korean Patent Nos. 259,367, and 315,630; and U.S. Pat. No. 6,319,984].
Moreover, the present inventors have developed the poly(organophosphazene)s with a functional group showing the sol-gel phase transition with change of temperature (Korean Patent application No. 2006-0005579).
A drug or bioactive molecule can be introduced to a poly(organophosphazene) with a functional group by a chemical bond such a covalent bond or coordinate covalent bond. The property of the poly(organophosphazene)s including biodistribution, biodegradation, pharmacodynamics, solubility, antigen reaction can be changed depending on the type of chemical bond.
A polymer-drug conjugate can control the emission of a drug, reduce the toxicity of a drug, and increase the medicinal effect according to the EPR effect (the effect of improved penetration and maintenance) [Bioconjugate Chem. 3, 351 (1992)]. As a representative study regarding drug delivery by such bonding, the cyclotriphosphazene-anticancer drug conjugate is known [J. Control. Release, 161, 55 (1998)].
A biodegradable and thermosensitive poly(organophosphazene) conjugated with a drug or bioactive molecule is the polymer-drug conjugate applied to the thermosensitive polymer. The poly(organophosphazene) conjugated with drug or bioactive molecule has the advantages of the polymer-drug conjugate and conventional drug carriers, so that it can effectively deliver the drug in vivo, have excellent medicinal effect, and become with the implantation type hydrogel which allows a cell to grow therein.
Moreover, the introduction of various additives to the polymer hydrogel can increase efficiency as the cell transfer material or drug. When delivering the polypeptide or the protein drug, the introduction of an additive can maintain the stability of the drug in the hydrogel, induce the ionic bonding of an additive and drugs, and control the release rate of medicine from hydrogel. Further, when delivering a treating cell, additives introduced to a hydrogel can increase the activity of a cell after being delivered into the body.